Apparatus and method for compensating for errors in temperature measurement of semiconductor wafers during rapid thermal processing

Abstract

The present invention is an apparatus for calibrating a temperature feedback value in a water processing chamber to automatically compensate for variations in infrared emissions from a heated semiconductor wafer due to variations in composition and coatings from wafer to wafer. A calibration wafer with an imbedded thermocouple is used to generate a table relating actual wafer temperatures to power supplied to the heating chamber and infrared emissions detected by a pyrometer. A sample wafer of a batch to be processed is subsequently placed in the chamber at a known power level, and any difference between the detected infrared emission value and the value in the table is used to adjust the entire table according to a first predetermined formula or table. Before each wafer is processed, a known source of infrared light is reflected off the wafer and detected. The reflected light value is compared to a reflection measurement for the sample wafer. The difference in reflection measurements is correlated to emissions from heating, and the calibration table is fine-tuned with the correlation value according to a second predetermined formula or table to account for variations in emissions between individual wafers due to variances in wafer surface conditions.

What is claimed is: 
     
       1. An apparatus for calibrating a processing signal derived from characteristics of a semiconductor wafer, comprising: a processing chamber having a range of temperature settings including means for holding a calibration wafer;   temperature measurement means coupled to the processing chamber for transmitting a signal indicating a temperature of said calibration wafer at a particular temperature setting;   light emission masurement means coupled to said processing chamber for measuring an amount of light emitted by said calibration wafer at said particular temperature setting; and   computer means for recording the amount of light emitted and temperature of said calibration wafer connected to the temperature measurement and light emission measurement means, including memory means for storing a first calibration table constructed from the measured light emission and temperature values used to determine a level of the processing signal, the computer means being programmed to recall and modify entries of the first calibration table according to light emission values of a sample batch wafer as measured by the light emission measurement means to generate a second calibration table and further programmed to calibrate said processing signal based on said entries of said second calibration table.   
     
     
       2. The apparatus of claim 1 wherein said computer means is programmed to provide said calibrated processing signal as a control signal to a power supply for said processing chamber. 
     
     
       3. The apparatus of claim 1 further comprising: light emission means for providing light to be reflected off of the sample batch wafer and a batch wafer;   reflection measurement means for measuring intensity of light reflected off of said sample batch wafer and said batch wafer and providing a reflection signal to said computer means; and   said computer means being programmed to modify said second calibration table in accordance with a difference in said reflection signal for said sample batch wafer and said batch wafer to generate a third calibration table.   
     
     
       4. The apparatus of claim 3 wherein said light emission means and said reflection measurement means are external to said processing chamber and further comprising a transfer arm for loading a particular wafer into said processing chamber and passing said particular wafer over said light emission means and reflection measurement means. 
     
     
       5. The apparatus of claim 3 wherein said light emission measurement means and said reflection means are infrared pyrometers. 
     
     
       6. An apparatus for calibrating a processing signal derived from characteristics of a semiconductor wafer, comprising: a processing chamber having a range of temperature settings including means for holding a calibration wafer;   temperature measurement means coupled to the processing chamber for transmitting a signal indicating the temperature of said calibration wafer;   light emission measurement means coupled to said processing chamber for measuring an amount of light emitted by said calibration wafer;   light emission means for providing light to be reflected off of a sample batch wafer and said calibration wafer;   reflection measurement means for measuring the intensity of said light reflected off of said sample batch wafer and said calibration wafer and providing a reflection signal; and   computer means for recording the amount of light emitted and temperature of said calibration wafer connected to the temperature measurement and light emission measurement means, including memory means for storing a first calibration table constructed from measured light emission and temperature values used to determine a level of the processing signal, the computer means being programmed to recall and modify the first calibration table in accordance with a difference in said reflection signal for said sample batch and calibration wafer to generate a second calibration table and to calibrate said processing signal based on said entries of said second calibration table.   
     
     
       7. An apparatus for calibrating a processing signal derived from characteristics of a semiconductor wafer, comprising: a processing chamber including means for holding said wafer;   a long arc lamp for heating said processing chamber to a range of temperature;   a power supply for said long arc lamp;   temperature measurement means coupled to the processing chamber for transmitting a signal from a thermocouple attached to a calibration wafer for indicating the temperature of the calibration wafer;   a first infrared pyrometer coupled to said processing chamber for measuring an amount of light emitted by the calibration wafer;   light emission means mounted outside said processing chamber for providing infrared light to be reflected off a particular wafer;   a second infrared pyrometer mounted outside said processing chamber for measuring the intensity of said light reflected off of said particular wafer and providing a reflection signal;   a transfer arm for loading said particular wafer into said processing chamber and passing said particular wafer over said light emission means and said second infrared pyrometer; and   computer means for recording the amount of light emitted and temperature of the calibration wafer connected to the temperature measurement and light emission measurement means, including memory means for storing a first calibration table constructed from the measured light emission and temperature values used to determine a level of the processing signal, the computer means being programmed to recall and modify entries of said first calibration table according to light emission values of a sample batch wafer as measured by the first pyrometer to generate a second calibration table, said computer means being programmed to modify a light emission value from said second pyrometer with said second calibration table and to provide a modified signal as a control signal to said power supply for said processing chamber, said computer means also being programmed to modify said second calibration table in accordance with a difference in said reflection signal between a batch wafer and one of said sample batch and calibration wafers to generate a third calibration table and to calibrate said processing signal based on said entries of said third calibration table.